Background: Intact orthostatic blood pressure regulation is essential for early mobilization after surgery. However,\npostoperative orthostatic hypotension and intolerance (OI) may delay early ambulation. The mechanisms of\npostoperative OI include impaired vasopressor responses relating to postoperative autonomic dysfunction. Thus,\nbased on a previous study on haemodynamic responses during mobilization before and after elective total hip\narthroplasty (THA), we performed secondary analyses of heart rate variability (HRV) and aimed to identify possible\nabnormal postoperative autonomic responses in relation to postural change.\nMethods: A standardized mobilization protocol before, 6 and 24 h after surgery was performed in 23 patients\nscheduled for elective THA. Beat-to-beat arterial blood pressure was measured by photoplethysmography and HRV\nwas derived from pulse wave interbeat intervals and analysed in the time and frequency domain as well as by\nnon-linear analysis using sample entropy\nResults: Before surgery, arterial pressures and HR increased upon standing, while HRV low (LF) and high frequency\n(HF) components remained unchanged. At 6 and 24 h after surgery, resting total HRV power, sample entropy and\npostural responses in arterial pressures decreased compared to preoperative conditions. During standing HF\nvariation increased by 16.7 (95 % CI 8.0ââ?¬â??25.0) normalized units (nu) at 6 h and 10.7 (2.0ââ?¬â??19.4) nu at 24 h compared\nto the preoperative evaluation. At 24 h the LF/HF ratio decreased from 1.8 (1.2ââ?¬â??2.6) nu when supine to 1.2 (0.8ââ?¬â??1.8)\nnu when standing.\nConclusions: This study observed postoperative autonomic cardiovascular dysregulation that may contribute to\nlimited HRV responses during early postoperative mobilization
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